The invention relates to transient voltage suppressors, and more particularly, to a transient voltage suppressor module that is contained in a housing similar in size and shape to a circuit breaker housing, and can be plugged into a circuit breaker or load distribution panel.
Protecting sensitive electronic equipment in homes and businesses from short duration voltage and current pulses caused by lightning or switching large currents into and out of commercial power lines, etc. presents a difficult challenge. To meet the challenge, a variety of commercially available pulse suppressor components, such as metal oxide varistors (MOV's), air gap or spark gap suppressors, and high power semiconductor pulse suppressors (such as the assignee's TRANSZORB devices) are widely used.
The concept of incorporating a surge protection device in a circuit-breaker-like housing is disclosed in U.S. Pat. No. 4,642,733. However, that reference does not provide any disclosure of a surge suppressor which, as a practical matter, can be enclosed within a housing of the same general size and shape as a conventional plug-in circuit breaker and is capable of meeting the so-called "10KA Category C requirements". (The "10KA Category C requirements" are established by ANSI/IEEE C62.41-1980, and require that the suppressor withstand both a 10 kiloampere current pulse having a rise time of approximately 8 microseconds and a fifty percent decay time of 20 microseconds. The 10KA Category C requirement also specifies that the suppressor be able to withstand a 6 kilovolt pulse having a rise time of 1.2 microseconds and a fifty percent decay time of 50 microseconds.) The cost and physical size limitations of currently available 10KA Category C surge suppressor devices and the need for them to reliably withstand a reasonably large number (i.e., approximately 50 or more) of 10 kiloampere transient current pulses presents a major design problem if it is necessary that the entire suppressor assembly be included in a small housing having dimensions of approximately three inches by three and one-half inches by three-fourths of an inch. This is the maximum practical size if the suppressor module is to be plugged into a single slot of a residential circuit breaker or load distribution panel.
A typical low cost 20 millimeter MOV is rated to survive only one 6.5 kiloampere current pulse, and typically would not survive even one 10 kiloampere current pulse. MOV's gradually degrade when subjected to current pulses within their rating, until they eventually fail by short circuiting. If an MOV short-circuits, it often explodes if an ordinary 110 volt AC line voltage then is applied across it. Consequently, "fail safe" fusing is necessary. No commercially available fuses are both capable of surviving a 10 kiloampere Category C pulse, and are small enough to fit into a housing that is roughly the size of a conventional plug-in circuit breaker.
The potential market for a surge suppressor module pluggable into a circuit breaker panel requires that it provide a readily observable indication of whether the module needs to be replaced.
Accordingly, there is an unmet need for a low cost, reliable transient voltage suppressor (TVS) module which meets the 10KA Category C requirements and can be plugged into a standard circuit breaker panel or the like.